Microelectromechanical systems (“MEMS”) are used in a growing number of applications. For example, MEMS currently are implemented as gyroscopes to detect pitch angles of airplanes, as microphones for use in mobile telephones, and as accelerometers to selectively deploy air bags in automobiles. In simplified terms, such MEMS devices typically have a structure suspended above a substrate, and associated electronics that both senses movement of the suspended structure and delivers the sensed movement data to one or more external devices (e.g., an external computer). The external device processes the sensed data to calculate the property being measured (e.g., pitch angle, incident acoustic signal, or acceleration).
As known by those skilled in the art, one commonly used technique for forming MEMS devices, known as “surface micromachining,” builds material layers on top of a substrate using additive and subtractive processes. The complexity of surface micromachining processes often increases, however, as more layers are added to and subtracted from the substrate. Thick layers, such as rigid backplates in a MEMS microphone, present further challenges to the micromachining process.